The present invention relates to distributor injection pumps. More particularly, the present invention relates to a high-pressure pump for supplying fuel to an internal combustion engine.
Because of continuously increasing requirements due to stricter exhaust regulations for gasoline engines and compression-ignited internal combustion engines, the point of injection, in particular for compression-ignited internal combustion engines, should be adjusted to the particular operating phase of the engine. In the cold-running phase, in particular at low outside temperatures, the point of injection may need to be advanced at diesel distributor injection pumps, thus making a low-emission start with reduced particle emission and reduced noise, as well as a subsequent emission-free cold-running phase possible. As the rotational speed of the internal combustion engine increases, the delivery start of the injection pump should be advanced in order to compensate for the time shift caused by delayed injection and ignition.
After the injection operation, diesel fuel may require a certain time period to pass from the liquid state into the gaseous state and, in this state, to form an ignitable mixture with the combustion air which self-ignites at high pressure. The time period between the injection start and combustion start is discussed in regards to compression-ignited internal combustion engines as ignition delay. The ignition delay is determined, among other factors, by the ignitability of the diesel fuel (expressed by the cetane number), the achievable compression ratio xcex5 of the compression-ignited internal combustion engine, and the quality of the fuel atomization by the injection nozzle of the fuel injector. The ignition delay of compression-ignited internal combustion engines is usually on the order of magnitude of 1 to 2 ms. During the cold-running phase at low outside temperatures, this time period becomes longer, resulting in soot production by the uncombusted fuel, which is discharged into the environment through the exhaust system.
In the case of distributor injection pumps of compression-ignited engines, different cold-start acceleration measures may be used. A hydraulic measure for start acceleration is to temporarily raise the internal pressure of the distributor injection pump during the cold start and during the immediately subsequent cold-running phase of compression-ignited internal combustion engines. As the internal pressure is raised, an injection start timing piston is displaced, resulting in the injection start being advanced. The disadvantage of this measure may be the subsequent loose run of the injection timing piston due to the slow increase in pressure in the interior of the distributor injection pump.
Another option for advancing the injection start is to advance the injection timing piston and thus the injection start by rotating a component designed as a roller ring during the start and during the cold-running phase of the compression-ignited internal combustion engine. Another measure for cold start acceleration which may be carried out using mechanical means is to displace the injection timing piston by pressing on one side of the injection timing piston using a cam shaft so that the injection start is advanced.
The above-mentioned measures may have the disadvantage that only a small amount of adjustment is possible, limited by the mechanical overstress of the components involved, and thus only a limited advance of the injection start is achievable.
FIG. 1 shows a high-pressure pump having an advance timing unit, as is conventional in the related art.
High-pressure pump 1 includes a housing 2, on whose lower side a timing unit 5 for displacing the point of injection is flange-connected. Timing unit 5 for displacing the point of injection includes a two-part housing, a gasket plate being inserted at a housing joint 40 between the halves of the housing of timing unit 5 and housing 2 of high-pressure pump 1.
Timing unit 5 for displacing the point of injection includes a displaceably mounted injection timing piston 6. A pivot bearing 7, which is used to receive a lever, is positioned inside injection timing piston 6. Using this lever, a roller ring of a high-pressure pump 1 may be adjusted within housing 2 in such a manner that the point of injection of fuel into the combustion chambers of an internal combustion engine is displaced.
This lever is also referred to as a timing pin of an injection timing piston for adjusting the roller ring.
The lever accommodated in pivot bearing 7 of injection timing piston 6 extends through an orifice 9 in the injection timing piston, which is dimensioned in such a manner that a pivoting movement of the lever of pivot bearing 7 within injection timing piston 6 is possible. Injection timing piston 6 is penetrated by a first inlet bore 10, which may run essentially in the vertical direction, and a second inlet bore 11, which may run essentially perpendicular to the first bore. Second inlet bore 11 discharges into a regulating slide bore 13, which may run essentially parallel to the axis of symmetry of injection timing piston 6. A piston-shaped regulating slide 12, which is provided on its face toward a cavity 24 with an outlet bore having an enlarged diameter, is introduced into regulating slide bore 13. Regulating slide 12 corresponds to a control piston and is also referred to in combination with injection timing piston 6 as a trailing or servo injection timing piston. There is a connection between a first channel 14, running transversely to the axis of symmetry of regulating slide 12, and a second channel 15 implemented in regulating slide 12, second channel 15 discharging in the region of regulating slide 12 which is implemented with an enlarged internal diameter. A slotted disk 16 is assigned to regulating slide 12 on its external circumference, which fixes the displacement path of regulating slide 12 running in the axial direction inside injection timing piston 6, the slotted disk forming a stop 22 for regulating slide 12.
Slotted disk 16 presses against second front face 18 of injection timing piston 6 inside a recess 19 of injection timing piston 6, while, in the state illustrated in FIG. 1, first front face 17 of injection timing piston 6 faces a housing delimitation wall of timing unit 5 for displacing the point of injection.
On its face toward a cavity 24, regulating slide 12 includes a support disk 20, which is used as a contact surface for a control spring 31. Control spring 31 is supported on inner side 26 of a cold-start accelerator piston 23. A disk 21 may be provided on inner side 26 of cold-start accelerator piston 23. Inner side 26 of cold-start accelerator piston 23 is additionally used as a stop surface for a first spring element 25, which is supported on an adapter plate 30 on the side diametrically opposed to inner side 26. An annular projection is implemented on adapter plate 30, which is used as a stop surface for second front face 18 of injection timing piston 6. In addition, a trailing piston/regulating slide retaining spring 32 is introduced between first spring element 25 and control spring 31. This retaining spring is supported on one side on the peripheral surface of slotted disk 16 on second front face 18 of injection timing piston 6 and on the other side on a sleeve body 34. Sleeve body 34, whose lateral surface includes individual orifices 35, has a first sleeve body stop 36 and a second sleeve body stop 37. Regulating slide/trailing piston retaining spring 32 is supported on one side on first sleeve body stop 36 and on the other side on slotted disk 16 in the region of second front face 18 of injection timing piston 6.
Face 27 of cold-start accelerator piston 23 illustrated here, which faces a pressure chamber 28, is supported on a stop 29 implemented on the housing wall of timing unit 5. An annular groove 38 is introduced into the peripheral surface of cold-start accelerator piston 23, which is connected via an outlet bore 39 to cavity 24, which is delimited by inner side 26 of cold-start accelerator piston 23, adapter plate 30, and second face 18 of injection timing piston 6 in the region of recess 19.
It may be disadvantageous in this exemplary embodiment of a high-pressure pump 1 for supplying a fuel injection system with fuel that a gap 33 exists between inner side 26 of cold-start accelerator piston 23 and first sleeve body stop 36. This gap 33 may have the effect that an uncontrolled movement of injection timing piston 6 may occur during the gradual pressure buildup in cavity 24 via inlet bores 10 and/or 11, first channel 14 and/or second channel 15 and the inner side of sleeve body 34, as well as orifices 35 implemented therein. Therefore, stable adjustment in the lower speed range of high-pressure pump 1 may be achieved with difficulty, since a clearance, which is dependent on the construction, may remain between first sleeve body stop 36 and the diametrically opposed section of inner side 26 of cold-start accelerator piston 23. Since second sleeve body stop 37 overlaps support disk 20 of regulating slide 12, the position of first sleeve body stop 36 of sleeve body 34 is fixed, due to which annular gap 33 is formed.
Using an exemplary embodiment of the present invention, a continuous application of pressure to an injection timing piston of a timing unit may be used for displacement of the injection curve. By moving the support point of a spring element which is applied directly to the injection timing piston from a movable component to a component which is stationary in the start phase, oscillation of this piston between two stop surfaces may be prevented through application to this injection timing piston. In this manner, an uncontrolled axial movement of the injection timing piston is prevented, which may favorably influence the material wear due to friction.
By integrating a spring assembly into the cavity of the timing unit for displacing the point of injection, which is delimited by the cold-start accelerator piston and the injection timing piston, two spring elements having different spring stiffnesses c1, c2 may be positioned on a displaceably mounted spring support ring. Spring stiffness c1 may be selected to be very small, this spring stiffness being responsible for the cold start, while spring stiffness c2 of the remaining spring element may be designed in regard to normal operation.
In the rest position of the high-pressure pump, i.e., when the internal combustion engine has not yet been started, the spring element of the spring assembly applied to the injection timing piston is prestressed, while the spring element assigned to the cold-start accelerator piston is in the unloaded position.
In an exemplary embodiment of the present invention in which a spring assembly in the form of two spring elements is connected in series between the cold-start accelerator piston and the injection timing piston, all injection timing piston control springs in accordance with a modular system may be used. By selecting the stiffness of the spring elements, the desired spring characteristics and therefore the curve of the prestress force may be adjusted depending on the application of the high-pressure pump. The spring element applied directly to the injection timing piston is designed in such a manner that all typical spring elements may be installed if this spring element is positioned directly on the cold-start accelerator piston. To support a first spring element, the spring element may be applied directly to the injection timing piston, and to support the spring elements of the spring assembly connected in series, a stepped arrangement of multiple contact surfaces may be implemented on the inner side of the cold-start accelerator piston. The individual contact surfaces for the spring elements may be implemented as ring surfaces.